Ethernet has seen use in a broad array of products. However, Ethernet requires a considerable amount of hardware and software to implement even a simple device.
A typical Ethernet device, even one with very simple functionality, requires the following components just to provide Ethernet communications (in addition to the actual function of the device):                1. Ethernet physical access layer (PHY) and related magnetics, connectors and other hardware.        2. Ethernet media access control (MAC) to communicate packets in digital form between the device and the PHY.        3. Packet memory to store received packets while they're evaluated and consumed and to store outgoing packets for transmission.        4. Microprocessor and software for evaluating a range of protocols communicated over the Ethernet. The protocols evaluated in an implementation would include some of the following, along with various other protocols:                    ARP (Address Resolution Protocol)            ICMP (Internet Control Message Protocol)            UDP (User Datagram Protocol)            TCP (Transmission Control Protocol)            DHCP (Dynamic Host Configuration Protocol)            BOOTP (Bootstrap Protocol)                        5. Ethernet switching apparatus for each device comprising either a port on a general switch for each device or switching resources on the individual device. The Ethernet switching apparatus requires additional memory and hardware logic resources, as well as additional software/protocol requirements for switch management.        
The components listed above are in addition to those required for the actual function of the Ethernet device.
The considerable amount of hardware and software to implement even an Ethernet simple device makes Ethernet cost prohibitive for certain classes of applications.
It is therefore highly desirable to provide an Ethernet interface or node that requires fewer components, is less complex and is of lower cost.